Graphene is typically defined to be a one-atom-thick, substantially planar sheet of sp2 bonded carbon atoms. Because of the sp2 bonding, the carbon atoms forming graphene are densely packed in a honeycomb crystalline lattice. Because of its electrical properties, graphene is being investigated as a possible replacement for silicon in electronic devices. There are several methods of forming graphene, including the drawing method (generally called micromechanical exfoliation or the Scotch tape method), epitaxial growth on silicon carbide, epitaxial growth on metal substrates, graphite oxide reduction, growth from metal-carbon melts, pyrolysis of sodium ethoxide, and through production from nanotubes.